The chain on an overhead conveyor is rarely the limiting component. The drive, the track and the hangers are, and all three are sized from a chain pull figure that is often estimated rather than calculated.
The chain pull equation, without the theatre
Chain pull is the sum of four terms: the friction of the loaded horizontal run, the friction of the return run, the lift on any incline, and the losses in curves and drive units.
For a horizontal run, friction is the moving weight multiplied by a friction factor. For an enclosed track chain on standard rollers, use 0.03 to 0.05; for an I-beam chain with worn wheels, 0.05 to 0.08. Add the product weight, the hanger weight and the chain weight per metre.
An incline adds the vertical lift directly: product weight times the height, with no friction factor. A curve adds 3 to 8 percent of the pull entering it, depending on radius. A drive unit adds 5 percent.
A worked example
A paint line carries 40 hangers at 12 kg each, spaced 1.2 m apart, on a 48 m closed loop with one 4 m incline and four 90-degree curves. Chain weight is 2.4 kg per metre.
- Product and hanger load: 40 x 12 = 480 kg
- Chain load: 48 x 2.4 = 115 kg
- Loaded horizontal friction at 0.04: (480 + 115) x 0.04 = 24 kgf
- Lift on the incline: only the four hangers actually on the 4 m ramp count, so 4 x 12 = 48 kgf
- Curve allowance at 5 percent of the accumulated pull: about 6 kgf
The result is a chain pull of roughly 80 kgf. With a service factor of 1.5 the drive is sized for 120 kgf. That number, not the 480 kg product load, is what the drive and track must survive.
The example is deliberately simple. The point is that the lift term is small when only a few hangers are on the incline, and that the friction term is smaller than most people assume. The corollary is that the drive is usually limited by starting torque and by the curve losses, not by the static weight.
Hanger spacing
Spacing is set by the product length and by the process, not by the chain. Two rules apply. First, the hanger must not allow the product to touch the one ahead on a curve; calculate the swept width at the tightest radius. Second, the spacing must be a multiple of the index pitch if the line stops at fixed positions.
On a coating line, spacing is also set by the oven: parts too close shield each other from airflow and cure unevenly. A 1.2 m spacing that works in the spray booth may be too tight in the oven.
Track and wheel selection
Enclosed track carries lighter loads at higher speed and is cleaner. I-beam track carries heavier loads, tolerates heat better and is easier to inspect. The crossover is roughly 60 kg per hanger; above that, I-beam is usually the safer choice.
Wheels are the consumable. Sealed ball-bearing wheels last longer in dusty plants; plain-bearing wheels tolerate heat and impact better. Specify which one you want, because suppliers substitute.
Drive sizing and service factor
Size the drive on the calculated pull at the slowest speed, then apply a service factor of 1.5 for uniform loads and 2.0 for shock loads or frequent starts. Check the starting torque separately: a loaded overhead line with a cold lubricant can need three times the running torque.
If the calculated pull is within 20 percent of the chain's working load, go up one chain size. Overhead failures are expensive because they happen above the production floor.
